CHICHAGOF COVE 



8l 



color than the mass. The rocks are much altered, the groundmass 

 largely to chlorite and bluish fibrous hornblende, the hornblende 

 pheiiocrysts to the same, with separation of magnetite grains on the 

 borders. The feldspar is cloudy with kaolin and indeterminable. 

 Some of the dark fragments prove to be aggregates of tourmaline 

 needles, others are more basic portions of the diorite-porphyrite. 

 These are apparently friction breccias formed near the border of the 

 intrusion. 



The Dikes 



Dikes cutting the sedimentary rocks are found in all 

 parts of the area studied but are especially numerous in 

 the vicinity of the laccolithic mass. They are never of 

 very great dimensions; a few reach a thickness of about 

 twenty feet, but those from four to ten feet in width are 

 most frequent. Their linear extent is rarely more than a 

 few hundred feet, although one was found which could be 

 traced continuously about half a mile. The dike rocks, 

 being in general much more resistant than the shales and 

 sandstones which they traverse, stand up in bold walls, 



Stepovak Beds Diorite PorphyritO Stepovak Bed* 



FIG. l8. DIAGRAMMATIC SECTION ON SOUTH FACE OF CHICHAGOF PEAK. 



sometimes fifteen or twenty feet high, as shown in the 

 annexed sketch (fig. 18); and on the shore they generally 

 stand out as prominent cliffs. 



The dikes have not been indicated on the sketch map. 

 In a general way they are radial to the dome-shaped uplift 

 of Chichagof Peak, and hence for the most part cut across 

 the strike of the sedimentary beds at high angles. This 

 was strikingly the case with the dozen or more dikes 

 found along the shore of West Cove, all of which are 



